Pulsation Dampener for Gas Compressors Having Selectable Size Choke Openings

ABSTRACT

A gas flow pressure pulsation dampener includes a sealed housing having an inlet port, an outlet port a center section disposed between the inlet port and the outlet port. A choke plate is rotatably disposed in the center section and has a plurality of different size openings disposed circumferentially about the plate. The plate is positioned in the center section so that the openings are placed between the inlet port and the outlet port. The size differences between the openings and the circumferential separation between adjacent openings are selected so that the plate always presents one full opening or parts of two openings between the inlet port and the outlet port. Means for rotating the choke plate are provided to select one of the choke openings to be disposed between the inlet port and the outlet port.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of measurement of flow rate of gas discharged from a compressor. More particularly, the invention relates to pulsation dampeners used to improve the accuracy of measurement of gas flow rates under variable compressor output conditions.

2. Background Art

Natural gas is typically transferred from producing wellbores to pipelines. The pipelines ultimately are arranged to distribute natural gas to end users. Flow measurement devices are located at places where custody of the gas changes, for example, in a producing field with gas produced from a number of wells to a gas transportation entity owned pipeline.

Compressors are commonly used to raise pressure of the gas from the “upstream” side pressure at custody transfer points to the downstream side pressure. In cases such as number of producing wells being connected single pipeline intake point, a typical combination would include a single flow measurement device connected between the pipeline intake and the compressor output.

There is a well understood measurement problem when measuring natural gas flow rates when a compressor is used as described above. This problem is referred to as square root error (“SRE”). The opening and closing of a valve used in the compressor compression causes a pulsating wave that strikes the primary measuring device and creates a false indication of increase in the flow rate.

One way known in the art to reduce or eliminate RSE is to install a choking plate between the compressor and the flow measurement device. The choking plate opening is usually selected as one half of the orifice size in the flow measurement device, wherein an orifice type gas meter is used. As an example, a 4 inch meter run (intake and outlet line diameters), and with a 1.5 inch orifice plate in the flow meter, a choke plate having an 0.75 inch opening would be installed upstream of the measurement device. Such selection of choke plate opening works in most operating conditions to reducing the amplitude of pressure pulsation to an acceptable level, typically about 2%.

The problem with the foregoing solution is that it is a disadvantage to the transferor (upstream custodian) of the gas. The choke opening, when selected according the foregoing formula, restricts flow much more than is typically required for most operating conditions. In such case, the gas transferor's (e.g., producer's) compressor has to work much harder because it is output restricted. In the case of compression having producing wells as the input, the wells cannot produce to capacity, making them vulnerable to “sanding” (entry of formation particles into the wellbore) and the wells would need to be reworked at considerable expense.

What is needed is a selectable opening choke that can be adjusted to the largest opening needed to reduce SRE to acceptable levels while restricting gas flow to the smalles extent consistent with acceptable levels of SRE.

SUMMARY OF THE INVENTION

A gas flow pressure pulsation dampener includes a sealed housing having an inlet port, an outlet port a center section disposed between the inlet port and the outlet port. A choke plate is rotatably disposed in the center section and has a plurality of different size openings disposed circumferentially about the plate. The plate is positioned in the center section so that the openings are placed between the inlet port and the outlet port. The size differences between the openings and the circumferential separation between adjacent openings are selected so that the plate always presents one full opening or parts of two openings between the inlet port and the outlet port. Means for rotating the plate are provided select one of the choke openings to be disposed between the inlet port and the outlet port.

A method for dampening pressure pulses in flowing gas for volume measurement includes measuring pressure downstream of a variable opening choke in the flowing gas stream using a pressure transducer that generates an electrical or optical signal in response to pressure. An amplitude of pressure variations in the flowing gas is determined from the measured pressure signal. An opening size of the choke is adjusted until the determined amplitude falls below a selected threshold.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut away view of an example pressure dampener according to the invention.

FIG. 2 is an assembled side view of the dampener of FIG. 1.

FIG. 3 shows an outlet port side view of the dampener of FIG. 1, specifically showing the outlet port and an indicator wheel.

FIG. 4 shows an example choke plate with various size flow openings.

FIG. 5 shows an expanded view of the indicator plate.

FIG. 6 shows an example of an automated version of the dampener.

DETAILED DESCRIPTION

A cut away view of an example pressure dampener according to the invention is shown in FIG. 1. The dampener 10 includes a housing 12 made from steel or similar high strength material assembled from an inlet half 12A and an outlet half 12B. The halves 12A, 12B may be held together in a sealed configuration by threaded fasteners 14 disposed in suitable openings in a flange-like portion of the housing 12. Such portion will be shown in and explained with reference to FIG. 3. The halves 12A, 12B can be sealed when engaged to each other by an o-ring 16 or other seal.

The housing 12, in the present example disposed in the outlet half 12B includes a substantially flat cylindrical surface recess 18 in which is disposed a generally flat, circular choke plate 24. The choke plate 24 is rotatable with respect to the housing 12 within the recess 18. The choke plate will be explained in more detail with reference to FIG. 4. The diameter of the recess 18 and choke plate 24 are selected so that the circumference of the choke plate 24 is disposed below the bottom of corresponding inlet 20 and outlet 22 ports in the housing 12. Thus, the choke plate 24 is disposed to completely fill a flow path between the inlet port 20 and the outlet port 22 in the housing 12.

The inlet port 20 and the outlet port 22 may be coupled to gas flow lines (not shown) using flange type connectors 12C, 12D respectively at each longitudinal end thereof. The diameter of the flange connectors 12C, 12D will depend on the designed flow capacity of the pressure pulsation dampener 10.

The choke plate 24 may be rotated by a keyed shaft 26. The keyed shaft may be sealed against the housing 12 by an o-ring 27 or other seal. The keyed shaft 26 may be keyed to an indicator plate 28 disposed outside the housing 12. The indicator plate 26 provides the dampener's user with a visual indication of which size opening in the choke plate 24 is disposed in the flow path. Openings in the choke plate will be further explained with reference to FIG. 4. The indicator plate 28 will be further explained with reference to FIG. 5. The indicator plate 28, and correspondingly the choke plate 24 may be locked in a particular rotational position by a set screw 29.

FIG. 2 shows an assembled side view of the dampener 10.

FIG. 3 shows an outlet port end view of the dampener 10. The keyed shaft 26 may be disposed roughly in the center of the halves of the housing 12, the center portions of which (that is, proximate the recess [18 in FIG. 1]) may form a roughly circular, flange shape. The relative position of the outlet port flange 12D and the outlet port 22 with respect to the keyed shaft 26 (and thus the center of rotation of the indicator plate 28 and correspondingly the choke plate [24 in FIG. 1]) is clearly shown in FIG. 3.

FIG. 4 shows an example of the choke plate 24. The choke plate 24 includes a plurality of openings 32A-32J disposed proximate the circumference of the choke plate, but radially inward thereof by enough distance so that the entirety of any one opening 32A-32J is disposed within the flow path (in this drawing in the outlet port 22 because the recess is in the outlet housing half) when the choke plate is suitably rotated.

The openings 32A-32J may be arranged in progressively larger sizes to accommodate different flow rates through the dampener (10 in FIG. 1). When flow increases, a larger opening may be selected, for example, manually, by the user rotating the keyed shaft (26 in FIG. 1). The plate 24 is provided with suitable key slots 30 to engage the keyed shaft (26 in FIG. 1). The form of coupling rotation from the shaft to the choke plate shown and explained herein is not a limitation on the scope of the present invention. It is within the scope of the invention for a shaft to be welded, bolted, splined or otherwise rotationally fixed to the shaft to enable the shaft to rotate the choke plate 24.

An important aspect of the arrangement of the openings 32A-32J is that when the choke plate 24 is rotated, at least one full opening or parts of two adjacent openings are always disposed in the flow path. Using such arrangement, flow through the dampener is never closed off. FIG. 5 shows the indicator plate 28 in more detail. The indicator plate 28 is also rotationally coupled to the keyed shaft 26 so that rotation of the choke plate (24 in FIG. 1) corresponds to rotation of the indicator plate 28. Indicators corresponding to the opening in the choke plate may be provided on the indicator plate. A stop pin 40 may be provided to disable rotation of the indicator plate 28, and thus the choke plate (24 in FIGS. 1 and 4) into any position which would close flow in the flow path.

In using the device explained above with reference to FIGS. 1 through 4, the choke plate opening size may be selected manually based on average measurements of flow rate or other measurement related to flow rate. The choke plate opening should be selected to be the largest one resulting in pressure pulses below a selected threshold amplitude, for example, 2 percent of the average pressure.

An automatic version of the dampener is shown in FIG. 6. A pressure transducer 64 measures pressure in the outlet port 22. The pressure transducer 64 may generate an electrical or optical signal corresponding to the gas pressure in the outlet port. The transducer 64 should have a response time enabling sampling of the highest frequency pressure pulses expected in the outlet port 22. A control unit 54 accepts signal input from the transducer 64. The signals from the transducer 64 may be digitized by an analog to digital converter (ADC) 62. Output from the ADC 62 may be conducted to a pulse height analyzer 60, which determines the amplitude of pressure pulses measured by the transducer 64. A controller 58, which may be a microprocessor is programmed to receive signals from the pulse height analyzer 60, and to send a control signal to a motor driver 56. The motor driver 56 controls rotation of a motor 50. The motor may include a worm gear 52 on its output shaft, in contact with corresponding gearing on the keyed shaft 26. The programming for the controller 54 may include instructions to cause the motor 50 to rotate to cause successively smaller openings in the choke plate 24 to be positioned in the flow path if the measured pressure pulses exceed a predetermined threshold amplitude. An example threshold amplitude is 2 percent of the average pressure, although other thresholds may be used depending on the sensitivity of the particular flow measuring device to pressure pulses. If the measured pressure pulses drop below the threshold amplitude, the instructions may cause the motor 50 to rotate to disposed successively larger openings in the choke plate 24 to be disposed in the choke plate until the pressure pulses are just below the threshold amplitude.

A pulsation dampener according to the various aspects of the invention may enable optimizing operation of a gas compressor and a flow measuring device disposed in the outlet stream of the compressor.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. A gas flow pressure pulsation dampener, comprising: a sealed housing having an inlet port, an outlet port a center section disposed between the inlet port and the outlet port; a choke plate rotatably disposed in the center section and having a plurality of different size openings disposed circumferentially about the plate, the plate positioned in the center section so that the openings are placed between the inlet port and the outlet port, the size differences between the openings and the circumferential separation between adjacent openings selected so that the plate always presents one full opening or parts of two openings between the inlet port and the outlet port; and means for rotating the choke plate to select one of the choke opening to be disposed between the inlet port and the outlet port.
 2. The pressure pulsation dampener of claim 1 wherein the means for rotating comprises a shaft rotationally fixed to the choke plate.
 3. The pressure pulsation dampener of claim 2 wherein the means for rotating further comprises: a pressure transducer in pressure communication with the outlet port; a controller in signal communication with the pressure transducer; and a motor electrically coupled to the motor, the motor rotationally coupled to a shaft, the shaft coupled to the plate to cause rotation thereof; wherein the controller is configured to detect amplitude of pressure pulses, and in response to the detected amplitude cause the motor to rotate the shaft until the detected amplitude falls below a selected threshold.
 4. The pressure pulsation dampener of claim 2 wherein the shaft is keyed to the plate.
 5. The pressure pulsation dampener of claim 1 further comprising an indicator plate disposed outside the housing rotationally coupled to the means for rotating, the indicator having indications thereon corresponding to the openings in the choke plate to indicate which choke opening is disposed between the inlet port and the outlet port.
 6. A method for dampening pressure pulses in flowing gas for volume measurement, comprising: measuring pressure downstream of a variable opening choke in the flowing gas stream using a pressure transducer that generates an electrical or optical signal in response to pressure; determining amplitude of pressure variations in the flowing gas from the measured pressure signal; changing an opening size of the choke until the determined amplitude falls below a selected threshold.
 7. The method of claim 6 wherein the changing opening size comprises rotating a plate having a plurality of differently sized openings into the flowing gas stream. 